Most people are aware that The Prisoner was filmed partly on location at Portmeirion, North Wales.
But what a lot of people don't know is that six episodes of the first series of Danger Man include filming at, or footage of Portmeirion.
In fact in the very first episode of Danger Man, 'View form the Villa', we see McGoohan driving his car through Portmeirion.

I often wonder if an 'adult' McGoohan had ever travelled abroad before his visit to Portmeirion, if not I can understand why the brightly coloured buildings and island-feel remained firmly in his mind and was chosen for the setting of his masterpiece 'The Prisoner'.
Or it could just be that Portmeirion was an easier, cheaper alternative than a further afield exotic location.

View from the Villa

After identifying the Italian village in the painting, Drake drives through Portmeirion to find the villa and the painting's artist.
In this episode it is obvious that McGoohan actually visited Portmeirion for filming as he is seen driving his car under 'Bridge House', temporarily stopping at 'Battery Square', before parking outside the 'Ship Shop'.

Under The Lake

Drake stays at a lakeside hotel in Germany with Von Klaus and his daughter.
In this episode McGoohan is seen jumping from a bathroom window of the Main Hotel building at Portmeirion, even performing his own stunts! Other Portmeirion locations seen include 'The Gate House' and 'Battery Square'.

Four other Episodes...

Above: The Honeymooners

Above: Find and Return

Above: The Journey Ends Halfway

Above: Bury the Dead

In the four other episodes of the first series, Portmeirion only features briefly and I believe most of the clips are from footage filmed earlier. Familiar locations seen include 'The Camera Obscura Tower' - part of 'White Horses', 'The Bristol Colonnade' and the 'Bell Tower'.

One thing I do find curious is why after having filmed 6 of the 39 thirty-minute episodes at Portmeirion is why none of the 47 fifty-minute episodes were filmed there. Maybe McGoohan wanted to keep his 'find' a well-guarded secret to add more mystery when it appeared on TV screens in The Prisoner?